Rust inhibitors for aqueous systems



United States, Patent ce a 2,726,215 RUST INHIBITORS non AQUEOUS sYsrEMsDonald T. Jones, Springfield, Pa., assignor to The Atlantic RefiningCompany,'Philadelphia, Pa., a corporation of Pennsylvania N Drawing.Application April 19, 1952, Serial No. 283,267

' This invention is directed to a method for suppressing the corrosionof metal surfaces in the presence of aqueous solutions. Moreparticularly, this invention is directed to the suppression of corrosionwhich occurs when ferrous metals are contacted with water, or aqueoussolutions containing dissolved salts or acids, or aqueous solutionswhich are admixed with non-aqueous solutions.

The hazards of corrosion which are involved when aqueous solutionscontact metal surfaces are well-known in every industry. Corrosion notonly causes replacement of metals, but also often results ,in'darnage toproducts by contamination, shutdown of production, loss of ethciency,and mechanical failure by weakening of theequipment. In addition,corrosion often loosens finely divided metal oxides which may act asoxidation catalysts increasing the rate of deterioration of variousorganic compounds with which they come in contact, or may enter betweenmoving parts of machinery where they act as abrasives. Even whencorrosion proceeds at a rather slow rate, continued corrosion over anextended period of time can be extremely serious and involve aconsiderable expense in both repair and replacement.

The increased cost of nearly all metals'during the last decade as wellas the difficulty of obtaining replacement equipment at any cost duringperiods of national emergency have stimulated efforts to minimizecorrosion problems. The serious nature of the problem is reflected bythe ever increasing amount of literature on both the broad and specificaspects of the subject.

One approach to the problem is to introduce a chemical into the fluidsolution which is to contact the metal surface in an effort to minimizecorrosion. Thousands of chemical compounds, both organic and inorganic,have been disclosed for this purpose, but the fact that none of thesecompounds has achieved universal acceptance in industry indicates thateach chemical compound has only a limited field of application.

t is therefore the main object of the present invention to provide aprocess whereby the corrosion of metallic surfaces in the presence ofaqueous solutions is materially inhibited. Another object of theinvention is to provide a method whereby the corrosion and rusting offerrous metals in the presence of aqueous solutions is materiallyinhibited. It is a further object of this invention to introducespecific organic salts into an aqueous solution to materially inhibitcorrosion of metallic surfaces by said solution.

In its broadest conception the invention is regarded as embracing theinhibition of the corrosion of metal surfaces in aqueous systems byintroducing particular salts of certain dicarboxylic acids in saidaqueous solutions.

More particularly, it has been found that the alkali and alkali earthmetal salts of certain dicarboxylic acids, namely, sebacic acid andazelaic acid, exhibit exceptional anti-corrosion powers whenincorporated in an aqueous solution which is to contact a metal surface.The unexpectedness of this invention resides in the fact that,

2,726,215 Patented nee. ,1955

although various dicarboxylic acids have been alluded for use in thepractice of the present invention are the alkalimetal salts, such as,lithium, sodium, or potassium, and the alkaline earth metal salts, suchas,.barium, .calcium, or magnesium.

The sebacic and azelaic acids which are employed to produce the saltsused in the present invention maybe obtained inany manner well-known tothe art. The

production of these acids has been fully discussed in both the chemicaland patent literature. For instance, a conventional method of preparingazelaic acid is by the oxidation of oleic acid, and sebacic acid can beprepared by heating a castor oil soap with NaOI-I, followed byhydrolysis.

Having described in detail the characteristics of the preferredanti-corrosion agent, the following examples Will illustrate certain ofthe numerous possible specific embodiments of the invention. Theexamples are intended to illustrate the invention and not to limit thesame as it is defined more broadly in the appended claims.

The eifectiveness of my composition in inhibitingthe corrosivity ofaqueous solutions may-be better and more fully understood by reference.to certain tests which have been conducted, using both water andaqueous solutions containing substances known to promote corrosion ofmetal, such as, inorganic chlorides, or sulfates, and acetic or sulfuricacids. The test procedure involved a measurement of the corrosive actionof these aqueous solutions, as inhibited with the novel compositions ofthis invention, upon thoroughly cleaned and sanded steel panels andsteel buttons, and a comparison thereof with the results obtained bysubjecting identical test strips and buttons to the corrosive action ofaqueous solutions not containing the anti-corrosion agent of the instantinvention. The steel buttons and panels were immersed in the abovementioned solutions at a temperature of about F. and observed daily forany evidence of rust.

It was not possible to dissolved more than .05% of sebacic acid or morethan .1% of azelaic in the distilled water. It will be observed from thedata in the foregoing table that when sebacic acid'or azelaic acid wereadded to the distilled water, there was practically no corrosioninhibition. However, when the alkali or alkali earth metal salts ofsebacic or azelaic acid were incorporated into the distilled water,corrosion inhibition was as much as 2000% greater. it is thusseen thatwhen the quantity of the alkali or alkali earth metal salts of sebacicor azelaic acid become greater than the corresponding molar quantity ofsebacic acid which can be dissolved, the rust inhibiting propertiesincreased tremendously.

Another series of runs, similar to those shown in Table 1,, wereconducted with aqueous solutions containing various substances known topromote rusting of iron and steel, such as, inorganic chlorides orsulfates and acetic or sulfuric acids. The results obtained in theseruns are set forth in Table II below:

Table II Composition of Test Solutions Number of Days t 7 Prior to RustInhibiting Agent Rust Promoting Agent Busting 3% Lithium AzelateSynthetic Sea Water 20+ 3% Sodium A'mlntp (in 7 None do 1 3% LithiumAzelete '0.1H%IzSO4 in Distilled 20+ 7 2 0.8% Barium azelate.- do 7+3.0% Sodium Azelate. do. 20+ None .do 1 3% Lithium Azclate 0.1% AceticAcid in Dis- 20% tilled H20. 0.8% Barium Azelate (1 7+ 3% Sodium Azelate10 None 1 Synthetic sea water: 11.0 g. MgClzfiHzO, 1.2 g. CaOlz, 4.0 g.NaaSOa, 25.0 g. NaCl per liter of distilled water.

It will be observed from the data presented in the foregoing table thatthe salts of this invention are capable of inhibiting corrosion of metalsurfaces in aqueous solutions which are normally considered to beextremely corrosive-the lithium salt of azelaic acid being particularlyeffective.

Additional corrosion inhibitors or anti-rusting compounds may also bepresent in some instances, as long as there is no chemical interactionbetween the two additives which would tend to diminish the efiectivenessof the salts of the present invention. Thus, in instances where a metalsurface is to contact a fluid medium which contains both water and oil,corrosion protective compositions which are particularly valuable in anoil medium may be used in conjunction with the additive of thisinvention, subject to the aforementioned limitations.

I claim:' 1. A method for reducing the corrosion of metals in contactwith aqueous solutions which comprises introducing into said aqueoussolution a minor but corrosioninhibiting amount of a salt selected fromthe group consisting of an alkalimet'al salt and an alkaline earth metalsalt of an acid selected from the group consisting of sebacic acid andazelaic acid.

2. The method according to claim 1, wherein the salt is an alkali metalsalt of azelaic acid.

3. The method according to claim 2, wherein the salt is lithium azelate.

4. The method according to claim 1, wherein the salt is sodium azelate.

5. The method according to claim 1, wherein the salt is an alkali earthmetal salt of azelaic acid.

6. The method according to claim 5, wherein the salt is barium azelate.

References Cited in the file of this patent UNITED STATES PATENTS

1. A METHOD FOR REDUCING THE CORROSION OF METALS IN CONTACT WITH AQUEOUSSOLUTIONS WHICH COMPRISES INTRODUCING INTO SAID AQUEOUS SOLUTION A MINORBUT CORROSIONINHIBITING AMOUNT OF A SALT SELECTED FROM THE GROUPCONSISTING OF AN ALKALI METAL SALT AND AN ALKALINE EARTH METAL SALT OFAN ACID SELECTED FROM THE GROUP CONSISTING OF SEBACIC ACID AZELAIC ACID.